Magnetic tape

ABSTRACT

The magnetic tape includes a non-magnetic support; and a magnetic layer including ferromagnetic powder and a binding agent on the non-magnetic support, in which a center line average surface roughness Ra measured regarding a surface of the magnetic layer is equal to or smaller than 1.8 nm, a logarithmic decrement acquired by a pendulum viscoelasticity test performed regarding the surface of the magnetic layer is equal to or smaller than 0.050, and a contact angle with respect to 1-bromonaphthalene measured regarding the surface of the magnetic layer is 45.0° to 55.0°.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C 119 to Japanese PatentApplication No. 2017-029502 filed on Feb. 20, 2017. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for storagesuch as data back-up. The recording and reproducing of information tothe magnetic tape are normally performed by allowing the magnetic tapeto run in a drive and bringing the surface of the magnetic layer of themagnetic tape to come into contact with a magnetic head (hereinafter,also simply referred to as a “head”) to slide thereon.

In the field of magnetic recording, the improvement of electromagneticconversion characteristics is constantly required. In regards to thispoint, JP2010-49731A, for example, discloses that a magnetic recordingmedium having excellent electromagnetic conversion characteristics isobtained by increasing surface smoothness of a magnetic layer (forexample, see paragraphs 0020 and 0178 of JP2010-49731A).

SUMMARY OF THE INVENTION

Increasing surface smoothness of a surface of a magnetic layer of amagnetic tape is an effective method for narrowing an interval (spacing)between a surface of a magnetic layer of a magnetic tape and a head toimprove electromagnetic conversion characteristics.

However, in such studies of the inventors, it was clear that a decreasein reproduction output is observed while repeating the running in themagnetic tape in which surface smoothness of the magnetic layer isincreased for improving electromagnetic conversion characteristics.

Therefore, an object of the invention is to provide a magnetic tapewhich shows excellent electromagnetic conversion characteristics and inwhich a decrease in reproduction output during repeated running isprevented.

According to one aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; and a magnetic layer includingferromagnetic powder and a binding agent on the non-magnetic support, inwhich a center line average surface roughness Ra measured regarding asurface of the magnetic layer is equal to or smaller than 1.8 nm, alogarithmic decrement acquired by a pendulum viscoelasticity testperformed regarding the surface of the magnetic layer is equal to orsmaller than 0.050, and a contact angle with respect to1-bromonaphthalene measured regarding the surface of the magnetic layeris 45.0° to 55.0°.

In the invention and the specification, the center line average surfaceroughness Ra measured regarding the surface of the magnetic layer of themagnetic tape (hereinafter, also simply referred to as a “magnetic layersurface roughness Ra”) is a value measured with an atomic forcemicroscope (AFM) in a region, of the surface of the magnetic layer,having an area of 40 μm×40 μm. As an example of the measurementconditions, the following measurement conditions can be used. Themagnetic layer surface roughness Ra shown in examples which will bedescribed later is a value obtained by the measurement under thefollowing measurement conditions. In addition, the “surface of themagnetic layer” of the magnetic tape is identical to the surface of themagnetic tape on the magnetic layer side.

The measurement is performed regarding the region of 40 μm×40 μm of thearea of the surface of the magnetic layer of the magnetic tape with anAFM (Nanoscope 4 manufactured by Veeco Instruments, Inc.) in a tappingmode. RTESP-300 manufactured by BRUKER is used as a probe, a scan speed(probe movement speed) is set as 40 μm/sec, and a resolution is set as512 pixel×512 pixel.

Hereinafter, the logarithmic decrement acquired by a pendulumviscoelasticity test performed regarding the surface of the magneticlayer is also simply referred to as “logarithmic decrement”.

In the invention and the specification, the logarithmic decrementdescribed above is a value acquired by the following method.

FIGS. 1 to 3 are explanatory diagrams of a measurement method of thelogarithmic decrement. Hereinafter, the measurement method of thelogarithmic decrement will be described with reference to the drawings.However, the aspect shown in the drawing is merely an example and theinvention is not limited thereto.

A measurement sample 100 is cut out from the magnetic tape which is ameasurement target. The cut-out measurement sample 100 is placed on asubstrate 103 so that a measurement surface (surface of the magneticlayer) faces upwards, in a sample stage 101 in a pendulumviscoelasticity tester, and the measurement sample is fixed by fixingtapes 105 in a state where obvious wrinkles which can be visuallyconfirmed are not generated.

A pendulum-attached columnar cylinder edge 104 (diameter of 4 mm) havingmass of 13 g is loaded on the measurement surface of the measurementsample 100 so that a long axis direction of the cylinder edge becomesparallel to a longitudinal direction of the measurement sample 100. Anexample of a state in which the pendulum-attached columnar cylinder edge104 is loaded on the measurement surface of the measurement sample 100as described above (state seen from the top) is shown in FIG. 1. In theaspect shown in FIG. 1, a holder and temperature sensor 102 is installedand a temperature of the surface of the substrate 103 can be monitored.However, this configuration is not essential. In the aspect shown inFIG. 1, the longitudinal direction of the measurement sample 100 is adirection shown with an arrow in the drawing, and is a longitudinaldirection of a magnetic tape from which the measurement sample is cutout. In the invention and the specification, the description regarding“parallel” includes a range of errors allowed in the technical field ofthe invention. For example, the range of errors means a range within±10° from an exact parallel state, and the error from the exact parallelstate is preferably within ±5° and more preferably within ±3°. Inaddition, as a pendulum 107 (see FIG. 2), a pendulum formed of amaterial having properties of being adsorbed to a magnet (for example,formed of metal or formed of an alloy) is used.

The temperature of the surface of the substrate 103 on which themeasurement sample 100 is placed is set to 80° C. by increasing thetemperature at a rate of temperature increase equal to or lower than 5°C./min (arbitrary rate of temperature increase may be set, as long as itis equal to or lower than 5° C./min), and the pendulum movement isstarted (induce initial vibration) by releasing adsorption between thependulum 107 and a magnet 106. An example of a state of the pendulum 107which performs the pendulum movement (state seen from the side) is shownin FIG. 2. In the aspect shown in FIG. 2, in the pendulumviscoelasticity tester, the pendulum movement is started by stopping(switching off) the electricity to the magnet (electromagnet) 106disposed on the lower side of the sample stage to release theadsorption, and the pendulum movement is stopped by restarting(switching on) the electricity to the electromagnet to cause thependulum 107 to be adsorbed to the magnetic 106. As shown in FIG. 2,during the pendulum movement, the pendulum 107 reciprocates theamplitude. From a result obtained by monitoring displacement of thependulum with a displacement sensor 108 while the pendulum reciprocatesthe amplitude, a displacement-time curve in which a vertical axisindicates the displacement and a horizontal axis indicates the elapsedtime is obtained. An example of the displacement-time curve is shown inFIG. 3. FIG. 3 schematically shows correspondence between the state ofthe pendulum 107 and the displacement-time curve. The stop (adsorption)and the pendulum movement are repeated at a regular measurementinterval, the logarithmic decrement A (no unit) is acquired from thefollowing Expression by using a displacement-time curve obtained in themeasurement interval after 10 minutes or longer (may be arbitrary time,as long as it is 10 minutes or longer) has elapsed, and this value isset as logarithmic decrement of the surface of the magnetic layer of themagnetic tape. The adsorption time of the first adsorption is set as 1second or longer (may be arbitrary time, as long as it is 1 second orlonger), and the interval between the adsorption stop and the adsorptionstart is set as 6 seconds or longer (may be arbitrary time, as long asit is 6 seconds or longer). The measurement interval is an interval ofthe time from the adsorption start and the next adsorption start. Inaddition, humidity of an environment in which the pendulum movement isperformed, may be arbitrary relative humidity, as long as the relativehumidity is 40% to 70%.

$\Delta = \frac{{\ln \left( \frac{A_{1}}{A_{2}} \right)} + {\ln \left( \frac{A_{2}}{A_{3}} \right)} + {\ldots \mspace{14mu} {\ln \left( \frac{A_{n}}{A_{n + 1}} \right)}}}{n}$

In the displacement-time curve, an interval between a point of theminimum displacement and a point of the next minimum displacement is setas a period of a wave. n indicates the number of waves included in thedisplacement-time curve in the measurement interval, and An indicatesthe minimum displacement and maximum displacement of the n-th wave. InFIG. 3, an interval between the minimum displacement of the n-th waveand the next minimum displacement is shown as Pn (for example, P₁regarding the first wave, P₂ regarding the second wave, and P₃ regardingthe third wave). In the calculation of the logarithmic decrement, adifference (in Expression A_(n+1), in the displacement-time curve shownin FIG. 3, A₄) between the minimum displacement and the maximumdisplacement appearing after the n-th wave is also used, but a partwhere the pendulum 107 stops (adsorption) after the maximum displacementis not used in the counting of the number of waves. In addition, a partwhere the pendulum 107 stops (adsorption) before the maximumdisplacement is not used in the counting of the number of waves, either.Accordingly, the number of waves is 3 (n=3) in the displacement-timecurve shown in FIG. 3.

Hereinafter, the contact angle with respect to 1-bromonaphthalene isalso referred to as a 1-bromonaphthalene contact angle. The1-bromonaphthalene contact angle is a value measured by a liquid dropletmethod. Specifically, the 1-bromonaphthalene contact angle is anarithmetical mean of values obtained by performing measurement regardinga certain sample six times by a θ/2 method in a measurement environmentof an atmosphere temperature of 25° C. and a relative humidity of 25%.An example of a specific aspect of measurement conditions will bedescribed later in examples.

In one aspect, the logarithmic decrement is 0.010 to 0.050.

In one aspect, the center line average surface roughness Ra is 1.2 nm to1.8 nm.

In one aspect, the contact angle with respect to the 1-bromonaphthalenemeasured regarding the surface of the magnetic layer is 45.0° to 53.0°.

In one aspect, the magnetic layer includes a nitrogen-containingpolymer.

In one aspect, the magnetic layer includes one or more lubricantsselected from the group consisting of fatty acid, fatty acid ester, andfatty acid amide.

In one aspect, the magnetic tape further comprises a non-magnetic layerincluding non-magnetic powder and a binding agent between thenon-magnetic support and the magnetic layer.

In one aspect, the magnetic tape further comprises a back coating layerincluding non-magnetic powder and a binding agent on a surface side ofthe non-magnetic support opposite to a surface side provided with themagnetic layer.

In the magnetic tape according to one aspect of the invention, it ispossible to exhibit excellent electromagnetic conversion characteristicsand prevent a decrease in reproduction output during repeated running.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram of a measurement method of alogarithmic decrement.

FIG. 2 is an explanatory diagram of the measurement method of alogarithmic decrement.

FIG. 3 is an explanatory diagram of the measurement method of alogarithmic decrement.

FIG. 4 shows an example (step schematic view) of a specific aspect of amagnetic tape manufacturing step.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Magnetic Tape Device

One aspect of the invention relates to a magnetic tape including: anon-magnetic support; and a magnetic layer including ferromagneticpowder and a binding agent on the non-magnetic support, in which acenter line average surface roughness Ra measured regarding the surfaceof the magnetic layer (magnetic layer surface roughness Ra) is equal toor smaller than 1.8 nm, a logarithmic decrement acquired by a pendulumviscoelasticity test performed regarding the surface of the magneticlayer is equal to or smaller than 0.050, and a contact angle withrespect to 1-bromonaphthalene measured regarding a surface of themagnetic layer (1-bromonaphthalene contact angle) is 45.0° to 55.0°.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer Surface Roughness Ra

The center line average surface roughness Ra measured regarding thesurface of the magnetic layer of the magnetic tape is equal to orsmaller than 1.8 nm. Accordingly, the magnetic tape can exhibitexcellent electromagnetic conversion characteristics. From a viewpointof further improving the electromagnetic conversion characteristics, themagnetic layer surface roughness Ra is preferably equal to or smallerthan 1.7 nm and even more preferably equal to or smaller than 1.6 nm. Inaddition, the magnetic layer surface roughness Ra can be equal to orgreater than 1.0 nm or equal to or greater than 1.2 nm. However, from aviewpoint of improving the electromagnetic conversion characteristics,low magnetic layer surface roughness Ra is preferable, and thus, themagnetic layer surface roughness Ra may be lower than the exemplifiedlower limit.

The magnetic layer surface roughness Ra can be controlled by awell-known method. For example, the magnetic layer surface roughness Racan be changed in accordance with the size of various powders includedin the magnetic layer or manufacturing conditions of the magnetic tape.Thus, by adjusting one or more of these, it is possible to obtain amagnetic tape having the magnetic layer surface roughness Ra equal to orsmaller than 1.8 nm.

The inventors have found that, in the magnetic tape having the magneticlayer surface roughness Ra equal to or smaller than 1.8 nm, in a casewhere any measures are not prepared, the reproduction output isdecreased while repeating running. Although the reason of a decrease inreproduction output is not clear, it is found that the decrease inreproduction output significantly occurs in a case of repeated runningof the magnetic tape at a high speed in an environment of a hightemperature and high humidity. The environment of a high temperature andhigh humidity here is, for example, an environment in which anatmosphere temperature is 30° C. to 45° C. and relative humidity isequal to or higher than 65% (for example, 65% to 90%). The running at ahigh speed is, for example, running of the magnetic tape at a runningspeed equal to or higher than 6.0 msec.

Therefore, as a result of intensive studies of the inventors, theinventors have newly found that it is possible to prevent a decrease inreproduction output during repeated running at a high speed in theenvironment of a high temperature and high humidity, by respectivelysetting the logarithmic decrement and the 1-bromonaphthalene contactangle as described above, in the magnetic tape having the magnetic layersurface roughness Ra equal to or smaller than 1.8 nm. Details of thispoint will be described later.

It is thought that the decrease in reproduction output occurs becausecomponents derived from the magnetic tape are attached to the head fromthe surface of the magnetic layer due to continuous sliding between thesurface of the magnetic layer and the head at the time of repeating therunning of the magnetic tape, and the attached components (hereinafter,referred to as “head attached materials”) exist between the surface ofthe magnetic layer and the head (so-called spacing loss). Thus, theinventors have made research for decreasing the amount of the componentsattached to the head from the surface of the magnetic layer. As aresult, the inventors have considered that the logarithmic decrement andthe 1-bromonaphthalene contact angle set as described above contributeto a decrease in amount of the components attached to the head from thesurface of the magnetic layer. The logarithmic decrement and the1-bromonaphthalene contact angle will be described later specifically.By doing so, the magnetic tape according to one aspect of the inventionhas been completed. However, the above and following descriptionsinclude the surmise of the inventors. The invention is not limited tosuch a surmise.

Logarithmic Decrement

The logarithmic decrement acquired by a pendulum viscoelasticity testperformed regarding the surface of the magnetic layer of the magnetictape is equal to or smaller than 0.050. This can contribute toprevention of a decrease in reproduction output, in a case of therepeated running of the magnetic tape having the magnetic layer surfaceroughness Ra in the range described above. From a viewpoint of furtherpreventing a decrease in reproduction output, the logarithmic decrementis preferably equal to or smaller than 0.048, more preferably equal toor smaller than 0.045, even more preferably equal to or smaller than0.040, and still more preferably equal to or smaller than 0.035. Inaddition, the logarithmic decrement can be, for example, equal to orgreater than 0.010 or equal to or greater than 0.012. From a viewpointof preventing a decrease in reproduction output, the logarithmicdecrement tends to be preferable, as it is low. Therefore, thelogarithmic decrement may be lower than the lower limit exemplifiedabove.

The inventors have considered regarding the logarithmic decrementdescribed above as follows. However, the below description is merely asurmise and the invention is not limited thereto.

It is possible to improve electromagnetic conversion characteristics byincreasing the surface smoothness of the surface of the magnetic layerof the magnetic tape. Meanwhile, it is thought that, in a case where thesurface smoothness is increased, a contact area (so-called real contactarea) between the surface of the magnetic layer and the head duringrepeated running increases. Accordingly, the inventors have surmisedthat components derived from the magnetic tape are easily attached tothe head from the surface of the magnetic layer and are attached andaccumulated on the head while repeating the running, thereby causingspacing loss which is a reason of a decrease in reproduction output.With respect to this, the inventors have thought that the componentsattached and accumulated on the head include pressure sensitive adhesivecomponents separated from the surface of the magnetic layer. Inaddition, the inventors have considered that the logarithmic decrementis a value which may be an index for the amount of the pressuresensitive adhesive components and the value equal to or smaller than0.050 means a decrease in amount of the pressure sensitive adhesivecomponents attached to the head from the surface of the magnetic layer.The details of the pressure sensitive adhesive components are not clear,but the inventors have surmised that the pressure sensitive adhesivecomponents may be derived from a resin used as a binding agent. Thespecific description is as follows. As a binding agent, various resinscan be used as will be described later in detail. The resin is a polymer(including a homopolymer or a copolymer) of two or more polymerizablecompounds and generally also includes a component having a molecularweight which is smaller than an average molecular weight (hereinafter,referred to as a “binding agent component having a low molecularweight”). The inventors have surmised that the binding agent componenthaving a low molecular weight which is separated from the surface of themagnetic layer during the running and attached and accumulated on thehead while repeating the running may cause the spacing loss which is areason of a decrease in reproduction output. The inventors have surmisedthat, the binding agent component having a low molecular weight may havepressure sensitive adhesive properties and the logarithmic decrementacquired by a pendulum viscoelasticity test may be an index for theamount of the component attached and accumulated on the head during therunning. In one aspect, the magnetic layer is formed by applying amagnetic layer forming composition including a curing agent in additionto ferromagnetic powder and a binding agent onto a non-magnetic supportdirectly or with another layer interposed therebetween, and performingcuring process. With the curing process here, it is possible to allow acuring reaction (crosslinking reaction) between the binding agent andthe curing agent. However, although the reason thereof is not clear, theinventors have considered that the binding agent component having a lowmolecular weight may have poor reactivity regarding the curing reaction.Accordingly, the inventors have surmised that the binding agentcomponent having a low molecular weight which hardly remains in themagnetic layer and is easily separated from the surface of the magneticlayer and attached to the head may be one of reasons for that thebinding agent component having a low molecular weight is attached andaccumulated on the head during the running.

A specific aspect of a method for adjusting the logarithmic decrementwill be described later.

1-Bromonaphthalene Contact Angle

The 1-bromonaphthalene contact angle measured regarding the surface ofthe magnetic layer of the magnetic tape is 45.0° to 55.0°. The inventorshave considered that, as a value of the 1-bromonaphthalene contact angleis small, affinity of the surface of the magnetic layer and the head ishigh, and as the value is great, the affinity of the surface of themagnetic layer and the head is low. The inventors have thought that thesurface of the magnetic layer showing the 1-bromonaphthalene contactangle of 45.0° to 55.0° can show excellent affinity with respect to thehead at the time of coming into contact with the head, and as a result,a stable contact state with respect to the head can be exhibited. It issurmised that this contributes to preventing cut scraps generated due tochipping of the surface of the magnetic layer at the time of sliding ofthe surface of the magnetic layer and the head, from becoming headattached materials causing the spacing loss which is a reason of adecrease in reproduction output. From a viewpoint of further preventinga decrease in reproduction output, the 1-bromonaphthalene contact anglemeasured regarding the surface of the magnetic layer is preferably equalto or greater than 45.5°, more preferably equal to or greater than46.0°, even more preferably equal to or greater than 46.5°, stillpreferably equal to or greater than 47.0°, and still more preferablyequal to or greater than 47.5°, and still even more preferably equal toor greater than 48.0°. In addition, from a viewpoint of manufacturingeasiness, the 1-bromonaphthalene contact angle measured regarding thesurface of the magnetic layer is preferably equal to or smaller than54.0°, more preferably equal to or smaller than 53.5°, even morepreferably equal to or smaller than 53.0°, still preferably equal to orsmaller than 52.5°, and still more preferably equal to or smaller than52.0°.

The 1-bromonaphthalene contact angle measured regarding the surface ofthe magnetic layer can be controlled by using a component capable ofadjusting the 1-bromonaphthalene contact angle (hereinafter, alsoreferred to as a “1-bromonaphthalene contact angle adjusting component”)and adjusting a content of such a component. For example, a value of the1-bromonaphthalene contact angle can be increased by using a componentwhich can exhibit an operation of increasing the value of the1-bromonaphthalene contact angle, as the 1-bromonaphthalene contactangle adjusting component, and increasing the content of the component.

As an example of the 1-bromonaphthalene contact angle adjustingcomponent, a lubricant can be used. In addition, a polymer which will bedescribed later specifically can also be used. For example, by using oneor more kinds of 1-bromonaphthalene contact angle adjusting componentsselected from the group consisting of the lubricant and the polymerwhich will be described later, it is possible to obtain the magnetictape in which the 1-bromonaphthalene contact angle measured regardingthe surface of the magnetic layer is 45.0° to 55.0°. In one aspect, itis possible to form a magnetic layer by using one or more lubricants areused as the 1-bromonaphthalene contact angle adjusting component,without using a polymer which will be described later. In anotheraspect, it is possible to form a magnetic layer by using one or morepolymers which will be described later as the 1-bromonaphthalene contactangle adjusting component, without using lubricants. In still anotheraspect, it is possible to form a magnetic layer by using one or morelubricants and one or more polymers which will be described latertogether as the 1-bromonaphthalene contact angle adjusting component.

1-Bromonaphthalene Contact Angle Adjusting Component

The 1-bromonaphthalene contact angle adjusting component is a componentcapable of adjusting the 1-bromonaphthalene contact angle measuredregarding the surface of the magnetic layer. Hereinafter, the1-bromonaphthalene contact angle adjusting component is also referred toas a 1-bromonaphthalene contact angle adjusting agent. Here, theexpression “capable of adjusting” means an operation of changing the1-bromonaphthalene contact angle can be exhibited. The exhibiting ofsuch an operation can be confirmed with a change in the1-bromonaphthalene contact angle measured regarding the surface of themagnetic layer in accordance with presence or absence of the1-bromonaphthalene contact angle adjusting component. The1-bromonaphthalene contact angle adjusting component preferably exhibitsan operation of increasing a value of the 1-bromonaphthalene contactangle. One aspect of the 1-bromonaphthalene contact angle adjustingcomponent is a lubricant, and another aspect thereof is a polymer whichwill be described later. Hereinafter, these components will be describedin order.

Lubricant

As the lubricant, various lubricants normally used in various magneticrecording media such as fatty acid, fatty acid ester, or fatty acidamide can be used. As the content of the lubricant included in themagnetic layer is great, a value of the 1-bromonaphthalene contact anglemeasured regarding the surface of the magnetic layer tends to increase.

Examples of fatty acid include lauric acid, myristic acid, palmiticacid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenicacid, erucic acid, and elaidic acid, and stearic acid, myristic acid,and palmitic acid are preferable, and stearic acid is more preferable.Fatty acid may be included in the magnetic layer in a state of salt suchas metal salt.

As fatty acid ester, esters of various fatty acids described above, forexample, butyl myristate, butyl palmitate, butyl stearate, neopentylglycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitantristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate,octyl stearate, isooctyl stearate, amyl stearate, and butoxyethylstearate can be used.

As fatty acid amide, amide of various fatty acid, for example, lauricacid amide, myristic acid amide, palmitic acid amide, and stearic acidamide can be used.

The content of fatty acid in the magnetic layer forming composition is,for example, 0 to 10.0 parts by mass, preferably 0.1 to 10.0 parts bymass, more preferably 0.5 to 8.0 parts by mass, and even more preferably1.0 to 7.0 parts by mass, with respect to 100.0 parts by mass of theferromagnetic powder. In a case of using two or more kinds of differentfatty acids as the fatty acid, the content thereof is the total contentthereof. The same applies to other components. That is, in the inventionand the specification, a given component may be used alone or used incombination of two or more kinds thereof, unless otherwise noted. In acase where two or more kinds of components are included as certaincomponents, the content of the component is a total content of the twoor more kinds thereof, unless otherwise noted.

The content of fatty acid ester is for example, 0.1 to 10.0 parts bymass, preferably 0.5 to 8.0 parts by mass, and more preferably 1.0 to7.0 parts by mass with respect to 100.0 parts by mass of theferromagnetic powder, as the content of fatty acid ester in the magneticlayer forming composition.

The content of fatty acid amide in the magnetic layer formingcomposition is, for example, 0 to 3.0 parts by mass, preferably 0 to 2.0parts by mass, and more preferably 0 to 1.0 part by mass with respect to100.0 parts by mass of the ferromagnetic powder.

In addition, in a case where the magnetic tape includes a non-magneticlayer between the non-magnetic support and the magnetic layer, thelubricant may or may not include in the non-magnetic layer. Normally, atleast some lubricant included in the non-magnetic layer moves to themagnetic layer side and can be present in the magnetic layer. Thecontent of fatty acid in the non-magnetic layer forming composition is,for example, 0 to 10.0 parts by mass, preferably 1.0 to 10.0 parts bymass, and more preferably 1.0 to 7.0 parts by mass with respect to 100.0parts by mass of the non-magnetic powder. The content of fatty acidester is, for example, 0 to 10.0 parts by mass and preferably 0.1 to 8.0parts by mass with respect to 100.0 parts by mass of the non-magneticpowder. The content of fatty acid amide in the non-magnetic layerforming composition is, for example, 0 to 3.0 parts by mass andpreferably 0 to 1.0 parts by mass with respect to 100.0 parts by mass ofthe non-magnetic powder.

Fatty acid and one or more derivatives of fatty acid are preferably usedin combination, one or more components selected from the groupconsisting of fatty acid ester and fatty acid amide, and fatty acid aremore preferably used in combination, and fatty acid, fatty acid ester,and fatty acid amide are even more preferably used in combination.

In a case where fatty acid and a derivative (ester and amide) of fattyacid are used in combination, a part derived from fatty acid of thefatty acid derivative preferably has a structure which is the same as orsimilar to that of fatty acid used in combination. As an example, in acase of using stearic acid as fatty acid, it is preferable to usestearic acid ester such as butyl stearate and/or stearic acid amide.

As the lubricant, a lubricant disclosed in a paragraph 0111 ofJP2009-96798A can be used.

Nitrogen-Containing Polymer

As one aspect of the 1-bromonaphthalene contact angle adjustingcomponent, a nitrogen-containing polymer can be used. It is assumed thata polymer chain included in the nitrogen-containing polymer contributesto an increase in 1-bromonaphthalene contact angle measured regardingthe surface of the magnetic layer. The nitrogen-containing polymer is apolymer including nitrogen atoms in a structure. Examples of preferablenitrogen-containing polymer include a polyalkyleneimine-based polymerwhich is one of amine-based polymer, and an amine-based polymer otherthan the polyalkyleneimine-based polymer. The polyalkyleneimine-basedpolymer is a polymer including one or more polyalkyleneimine chains. Fordetails of the polyalkyleneimine-based polymer, descriptions disclosedin paragraphs 0035 to 0077 of JP2016-51493A can be referred to. Inaddition, for details of the amine-based polymer, descriptions disclosedin paragraphs 0078 to 0080 of JP2016-51493A can be referred to.

In addition, in one aspect, the nitrogen-containing polymer ispreferably a polymer in which a weight-average molecular weight is in arange not exceeding a weight-average molecular weight of a binding agentincluded in the magnetic layer. For example, the weight-averagemolecular weight of the nitrogen-containing polymer can be equal to orsmaller than 80,000, equal to or smaller than 60,000, equal to orsmaller than 40,000, equal to or smaller than 35,000, equal to orsmaller than 30,000, equal to or smaller than 20,000, or equal to orsmaller than 10,000. In addition, the weight-average molecular weight ofthe nitrogen-containing polymer can be, for example, equal to or greaterthan 1,000, equal to or greater than 1,500, equal to or greater than2,000, or equal to or greater than 3,000. The weight-average molecularweight in the invention and the specification is a value obtained byperforming polystyrene conversion of a value measured by gel permeationchromatography (GPC), unless otherwise noted. As the measurementconditions, the following conditions can be used. The weight-averagemolecular weight shown in examples which will be described later is avalue obtained by performing polystyrene conversion of a value measuredunder the following measurement conditions, unless otherwise noted.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

In a case of adjusting the 1-bromonaphthalene contact angle measuredregarding the surface of the magnetic layer by using thenitrogen-containing polymer, the content of the nitrogen-containingpolymer in the magnetic layer is preferably equal to or greater than 0.5parts by mass and more preferably equal to or greater than 1.0 part bymass with respect to 100.0 parts by mass of the ferromagnetic powder.From a viewpoint of high-density recording, it is preferable that thecontent of other components in the magnetic layer is relatively low, inorder to increase a filling percentage of the ferromagnetic powder. Fromthis viewpoint, the content of the nitrogen-containing polymer in themagnetic layer is preferably equal to or smaller than 50.0 parts bymass, more preferably equal to or smaller than 40.0 parts by mass, evenmore preferably equal to or smaller than 30.0 parts by mass, stillpreferably equal to or smaller than 20.0 parts by mass, and still morepreferably equal to or smaller than 15.0 parts by mass, with respect to100.0 parts by mass of ferromagnetic powder.

In addition, for the controlling method of the 1-bromonaphthalenecontact angle, descriptions disclosed in paragraphs 0095 to 0098 ofJP2016-51493A can be referred to.

Next, the magnetic layer and the like of the magnetic tape will bedescribed more specifically.

Magnetic Layer

Ferromagnetic Powder

As the ferromagnetic powder included in the magnetic layer,ferromagnetic powder normally used in the magnetic layer of variousmagnetic recording media can be used. It is preferable to useferromagnetic powder having a small average particle size, from aviewpoint of improvement of recording density of the magnetic tape. Fromthis viewpoint, ferromagnetic powder having an average particle sizeequal to or smaller than 50 nm is preferably used as the ferromagneticpowder. Meanwhile, the average particle size of the ferromagnetic powderis preferably equal to or greater than 10 nm, from a viewpoint ofstability of magnetization.

As a preferred specific example of the ferromagnetic powder,ferromagnetic hexagonal ferrite powder can be used. An average particlesize of the ferromagnetic hexagonal ferrite powder is preferably 10 nmto 50 nm and more preferably 20 nm to 50 nm, from a viewpoint ofimprovement of recording density and stability of magnetization. Fordetails of the ferromagnetic hexagonal ferrite powder, descriptionsdisclosed in paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134to 0136 of JP2011-216149A, and paragraphs 0013 to 0030 of JP2012-204726Acan be referred to, for example.

As a preferred specific example of the ferromagnetic powder,ferromagnetic metal powder can also be used. An average particle size ofthe ferromagnetic metal powder is preferably 10 nm to 50 nm and morepreferably 20 nm to 50 nm, from a viewpoint of improvement of recordingdensity and stability of magnetization. For details of the ferromagneticmetal powder, descriptions disclosed in paragraphs 0137 to 0141 ofJP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A can bereferred to, for example.

In the invention and the specification, average particle sizes ofvarious powder such as the ferromagnetic powder and the like are valuesmeasured by the following method with a transmission electronmicroscope, unless otherwise noted.

The powder is imaged at a magnification ratio of 100,000 with atransmission electron microscope, the image is printed on printing paperso that the total magnification of 500,000 to obtain an image ofparticles configuring the powder. A target particle is selected from theobtained image of particles, an outline of the particle is traced with adigitizer, and a size of the particle (primary particle) is measured.The primary particle is an independent particle which is not aggregated.

The measurement described above is performed regarding 500 particlesarbitrarily extracted. An arithmetical mean of the particle size of 500particles obtained as described above is an average particle size of thepowder. As the transmission electron microscope, a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. can be used, forexample. In addition, the measurement of the particle size can beperformed by well-known image analysis software, for example, imageanalysis software KS-400 manufactured by Carl Zeiss. The averageparticle size shown in examples which will be described later is a valuemeasured by using transmission electron microscope H-9000 manufacturedby Hitachi, Ltd. as the transmission electron microscope, and imageanalysis software KS-400 manufactured by Carl Zeiss as the imageanalysis software, unless otherwise noted. In the invention and thespecification, the powder means an aggregate of a plurality ofparticles. For example, the ferromagnetic powder means an aggregate of aplurality of ferromagnetic particles. The aggregate of the plurality ofparticles not only includes an aspect in which particles configuring theaggregate directly come into contact with each other, and also includesan aspect in which a binding agent or an additive which will bedescribed later is interposed between the particles. A term “particles”is also used for describing the powder.

As a method of collecting a sample powder from the magnetic tape inorder to measure the particle size, a method disclosed in a paragraph of0015 of JP2011-048878A can be used, for example.

In the invention and the specification, unless otherwise noted, (1) in acase where the shape of the particle observed in the particle imagedescribed above is a needle shape, a fusiform shape, or a columnar shape(here, a height is greater than a maximum long diameter of a bottomsurface), the size (particle size) of the particles configuring thepowder is shown as a length of a long axis configuring the particle,that is, a long axis length, (2) in a case where the shape of theparticle is a planar shape or a columnar shape (here, a thickness or aheight is smaller than a maximum long diameter of a plate surface or abottom surface), the particle size is shown as a maximum long diameterof the plate surface or the bottom surface, and (3) in a case where theshape of the particle is a sphere shape, a polyhedron shape, or anunspecified shape, and the long axis configuring the particles cannot bespecified from the shape, the particle size is shown as an equivalentcircle diameter. The equivalent circle diameter is a value obtained by acircle projection method.

In addition, regarding an average acicular ratio of the powder, a lengthof a short axis, that is, a short axis length of the particles ismeasured in the measurement described above, a value of (long axislength/short axis length) of each particle is obtained, and anarithmetical mean of the values obtained regarding 500 particles iscalculated. Here, unless otherwise noted, in a case of (1), the shortaxis length as the definition of the particle size is a length of ashort axis configuring the particle, in a case of (2), the short axislength is a thickness or a height, and in a case of (3), the long axisand the short axis are not distinguished, thus, the value of (long axislength/short axis length) is assumed as 1, for convenience.

In addition, unless otherwise noted, in a case where the shape of theparticle is specified, for example, in a case of definition of theparticle size (1), the average particle size is an average long axislength, in a case of the definition (2), the average particle size is anaverage plate diameter, and an average plate ratio is an arithmeticalmean of (maximum long diameter/thickness or height). In a case of thedefinition (3), the average particle size is an average diameter (alsoreferred to as an average particle diameter).

The content (filling percentage) of the ferromagnetic powder of themagnetic layer is preferably 50 to 90 mass % and more preferably 60 to90 mass %. The components other than the ferromagnetic powder of themagnetic layer are at least a binding agent and one or more kinds ofadditives may be arbitrarily included. A high filling percentage of theferromagnetic powder in the magnetic layer is preferable from aviewpoint of improvement recording density.

Binding Agent

The magnetic tape is a coating type magnetic tape, and the magneticlayer includes a binding agent together with the ferromagnetic powder.As the binding agent, one or more kinds of resin is used. The resin maybe a homopolymer or a copolymer. As the binding agent, various resinsnormally used as a binding agent of the coating type magnetic recordingmedium can be used. For example, as the binding agent, a resin selectedfrom a polyurethane resin, a polyester resin, a polyamide resin, a vinylchloride resin, an acrylic resin obtained by copolymerizing styrene,acrylonitrile, or methyl methacrylate, a cellulose resin such asnitrocellulose, an epoxy resin, a phenoxy resin, and a polyvinylalkylalresin such as polyvinyl acetal or polyvinyl butyral can be used alone ora plurality of resins can be mixed with each other to be used. Amongthese, a polyurethane resin, an acrylic resin, a cellulose resin, and avinyl chloride resin are preferable. These resins can be used as thebinding agent even in the non-magnetic layer and/or a back coating layerwhich will be described later. For the binding agent described above,description disclosed in paragraphs 0028 to 0031 of JP2010-24113A can bereferred to. An average molecular weight of the resin used as thebinding agent can be, for example, 10,000 to 200,000 as a weight-averagemolecular weight.

In addition, a curing agent can also be used together with the bindingagent. As the curing agent, in one aspect, a thermosetting compoundwhich is a compound in which a curing reaction (crosslinking reaction)proceeds due to heating can be used, and in another aspect, aphotocurable compound in which a curing reaction (crosslinking reaction)proceeds due to light irradiation can be used. At least a part of thecuring agent is included in the magnetic layer in a state of beingreacted (crosslinked) with other components such as the binding agent,by proceeding the curing reaction in the magnetic layer forming step.The preferred curing agent is a thermosetting compound, polyisocyanateis suitable. For details of the polyisocyanate, descriptions disclosedin paragraphs 0124 and 0125 of JP2011-216149A can be referred to, forexample. The amount of the curing agent can be, for example, 0 to 80.0parts by mass with respect to 100.0 parts by mass of the binding agentin the magnetic layer forming composition, and is preferably 50.0 to80.0 parts by mass, from a viewpoint of improvement of strength of eachlayer such as the magnetic layer.

Other Components

The magnetic layer may include one or more kinds of additives, ifnecessary, together with the various components described above. As theadditives, a commercially available product can be suitably selected andused according to the desired properties. Alternatively, a compoundsynthesized by a well-known method can be used as the additives. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include a dispersing agent, a dispersing assistant, anantibacterial agent, an antistatic agent, an antioxidant, and carbonblack.

As an example of the additive, non-magnetic powder can be used. Oneaspect of the non-magnetic powder is non-magnetic powder which canfunction as an abrasive (hereinafter, referred to as an “abrasive”). Themagnetic layer including an abrasive can include a dispersing agentdisclosed in paragraphs 0012 to 0022 of JP2013-131285A, in order toimprove dispersibility of the abrasive. For the details of the abrasive,descriptions disclosed in paragraphs 0023 and 0024 of JP2013-131285A canalso be referred to.

One aspect of the non-magnetic powder is non-magnetic filler(hereinafter, referred to as a “projection formation agent”) which canfunction as a projection formation agent which forms projectionssuitably protruded from the surface of the magnetic layer. As theprojection formation agent, inorganic oxide powder, inorganic oxidecolloidal particles, and the like can be used. In the invention and thespecification, the “colloidal particles” are particles which are notprecipitated and dispersed to generate a colloidal dispersion, in a casewhere 1 g of the particles is added to 100 mL of at least one organicsolvent of at least methyl ethyl ketone, cyclohexanone, toluene, orethyl acetate, or a mixed solvent including two or more kinds of thesolvent described above at an arbitrary mixing ratio. For details of theprojection formation agent, descriptions disclosed in paragraphs 0013 to0028 of JP2011-048878A can be referred to. The average particle size ofthe colloidal silica (silica colloidal particles) shown in the exampleswhich will be described later is a value obtained by a method disclosedin a paragraph 0015 of JP2011-048878A as a measurement method of anaverage particle diameter, and a coefficient of variation showing theexamples which will be described later is a value obtained by a methoddisclosed in the same paragraph. A sphericity showing in the exampleswhich will be described later is a value obtained by a method disclosedin a paragraph 0020 of JP2011-048878A as a measurement method of acircularity. In the other aspect, the projection formation agent ispreferably carbon black.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on a non-magnetic support, or mayinclude a non-magnetic layer including non-magnetic powder and a bindingagent between the non-magnetic support and the magnetic layer. Thenon-magnetic powder used in the non-magnetic layer may be powder ofinorganic substances (inorganic powder) or powder of organic substances(organic powder). In addition, carbon black and the like can be used.Examples of the inorganic powder include powder of metal, metal oxide,metal carbonate, metal sulfate, metal nitride, metal carbide, and metalsulfide. These non-magnetic powder can be purchased as a commerciallyavailable product or can be manufactured by a well-known method. Fordetails thereof, descriptions disclosed in paragraphs 0146 to 0150 ofJP2011-216149A can be referred to. For carbon black which can be used inthe non-magnetic layer, descriptions disclosed in paragraphs 0040 and0041 of JP2010-24113A can be referred to. The content (fillingpercentage) of the non-magnetic powder of the non-magnetic layer ispreferably 50 to 90 mass % and more preferably 60 to 90 mass %.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support will be described. As the non-magneticsupport (hereinafter, also simply referred to as a “support”),well-known components such as polyethylene terephthalate, polyethylenenaphthalate, polyamide, polyamide imide, aromatic polyamide subjected tobiaxial stretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heatingtreatment may be performed with respect to these supports in advance.

Back Coating Layer

The magnetic tape can also include a back coating layer includingnon-magnetic powder and a binding agent on a surface side of thenon-magnetic support opposite to a surface provided with the magneticlayer. The back coating layer preferably includes any one or both ofcarbon black and inorganic powder. In regards to the binding agentincluded in the back coating layer and various additives which can bearbitrarily included in the back coating layer, a well-known technologyregarding the treatment of the magnetic layer and/or the non-magneticlayer can be applied.

Various Thickness

A thickness of the non-magnetic support is preferably 3.00 to 6.00 μm.

A thickness of the magnetic layer is preferably equal to or smaller than0.15 μm and more preferably equal to or smaller than 0.10 μm, from aviewpoint of realization of high-density recording required in recentyears. The thickness of the magnetic layer is even more preferably 0.01to 0.10 μm. The magnetic layer may be at least single layer, themagnetic layer may be separated into two or more layers having differentmagnetic properties, and a configuration of a well-known multilayeredmagnetic layer can be applied. A thickness of the magnetic layer in acase where the magnetic layer is separated into two or more layers is atotal thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.10 to 1.50 μmand is preferably 0.10 to 1.00 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.90 μm and even more preferably 0.10 to 0.70 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scanning electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are arbitrarilyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Each composition for forming the magnetic layer, the non-magnetic layer,or the back coating layer normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among those, from a viewpoint ofsolubility of the binding agent normally used in the coating typemagnetic recording medium, each layer forming composition preferablyincludes one or more ketone solvents such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of the solvent of each layerforming composition is not particularly limited, and can be set to bethe same as that of each layer forming composition of a typical coatingtype magnetic recording medium. In addition, steps of preparing eachlayer forming composition generally include at least a kneading step, adispersing step, and a mixing step provided before and after thesesteps, if necessary. Each step may be divided into two or more stages.All of raw materials used in the invention may be added at an initialstage or in a middle stage of each step. In addition, each raw materialmay be separately added in two or more steps. In the preparation of themagnetic layer forming composition, it is preferable that theferromagnetic powder and the abrasive are separately dispersed asdescribed above. In addition, in order to manufacture the magnetic tape,a well-known manufacturing technology can be used. In the kneading step,an open kneader, a continuous kneader, a pressure kneader, or a kneaderhaving a strong kneading force such as an extruder is preferably used.The details of the kneading processes of these kneaders are disclosed inJP1989-106338A (JP-H01-106338A) and JP1989-79274A (JP-H01-79274A). Inaddition, in order to disperse each layer forming composition, glassbeads and one or more kinds of other dispersion beads can be used as adispersion medium. As such dispersion beads, zirconia beads, titaniabeads, and steel beads which are dispersion beads having high specificgravity are suitable. The dispersion beads can be used by optimizing aparticle diameter (bead diameter) and a filling percentage of thedispersion beads. As a dispersing machine, a well-known dispersingmachine can be used. Each layer forming composition may be filtered by awell-known method before performing the coating step. The filtering canbe performed by using a filter, for example. As the filter used in thefiltering, a filter having a hole diameter of 0.01 to 3 μm can be used,for example.

Coating Step, Cooling Step, Heating and Drying Step, BurnishingTreatment Step, and Curing Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the non-magnetic support or performingmultilayer coating of the magnetic layer forming composition with thenon-magnetic layer forming composition in order or at the same time. Fordetails of the coating for forming each layer, a description disclosedin a paragraph 0066 of JP2010-231843A can be referred to.

In a preferred aspect, a magnetic layer can be formed through a magneticlayer forming step including a coating step of applying a magnetic layerforming composition including ferromagnetic powder, a binding agent, acuring agent, and a solvent onto a non-magnetic support directly or withanother layer interposed therebetween, to form a coating layer, aheating and drying step of drying the coating layer by a heatingprocess, and a curing step of performing a curing process with respectto the coating layer. The magnetic layer forming step preferablyincludes a cooling step of cooling the coating layer between the coatingstep and the heating and drying step, and more preferably includes aburnishing treatment step of performing a burnishing treatment withrespect to the surface of the coating layer between the heating anddrying step and the curing step.

The inventors have thought that it is preferable that the cooling stepand the burnishing treatment step in the magnetic layer forming step, inorder to set the logarithmic decrement to be equal to or smaller than0.050. More specific description is as follows.

The inventors have surmised that performing the cooling step of coolingthe coating layer between the coating step and the heating and dryingstep contributes to causing pressure sensitive adhesive componentseparated from the surface of the magnetic layer in a case where thehead comes into contact with and slides on the surface of the magneticlayer, to be localized in the surface and/or a surface layer part in thevicinity of the surface of the coating layer. The inventors havesurmised that this is because the pressure sensitive adhesive componentat the time of solvent volatilization in the heating and drying step iseasily moved to the surface and/or the surface layer part of the coatinglayer, by cooling the coating layer of the magnetic layer formingcomposition before the heating and drying step. However, the reasonthereof is not clear. In addition, the inventors have thought that thepressure sensitive adhesive component can be removed by performing theburnishing treatment with respect to the surface of the coating layer inwhich the pressure sensitive adhesive component is localized on thesurface and/or surface layer part. The inventors have surmised thatperforming the curing step after removing the pressure sensitiveadhesive component contributes setting the logarithmic decrement to beequal to or smaller than 0.050. However, this is merely a surmise, andthe invention is not limited thereto.

As described above, multilayer coating of the magnetic layer formingcomposition can be performed with the non-magnetic layer formingcomposition in order or at the same time. In a preferred aspect, themagnetic tape can be manufactured by successive multilayer coating. Amanufacturing step including the successive multilayer coating can bepreferably performed as follows. The non-magnetic layer is formedthrough a coating step of applying a non-magnetic layer formingcomposition onto a non-magnetic support to form a coating layer, and aheating and drying step of drying the formed coating layer by a heatingprocess. In addition, the magnetic layer is formed through a coatingstep of applying a magnetic layer forming composition onto the formednon-magnetic layer to form a coating layer, and a heating and dryingstep of drying the formed coating layer by a heating process.

Hereinafter, a specific aspect of the manufacturing method of themagnetic tape will be described with reference to FIG. 4. However, theinvention is not limited to the following specific aspect.

FIG. 4 is a step schematic view showing a specific aspect of a step ofmanufacturing the magnetic tape including a non-magnetic layer and amagnetic layer in this order on one surface of a non-magnetic supportand including a back coating layer on the other surface thereof. In theaspect shown in FIG. 4, an operation of sending a non-magnetic support(elongated film) from a sending part and winding the non-magneticsupport around a winding part is continuously performed, and variousprocesses of coating, drying, and orientation are performed in each partor each zone shown in FIG. 4, and thus, it is possible to sequentiallyform a non-magnetic layer and a magnetic layer on one surface of therunning non-magnetic support by multilayer coating and to form a backcoating layer on the other surface thereof. Such a manufacturing methodcan be set to be identical to the manufacturing method normallyperformed for manufacturing a coating type magnetic recording medium,except for including a cooling zone in the magnetic layer forming stepand including the burnishing treatment step before the curing process.

The non-magnetic layer forming composition is applied onto thenon-magnetic support sent from the sending part in a first coating part(coating step of non-magnetic layer forming composition).

After the coating step, in a first heating process zone, the coatinglayer of the non-magnetic layer forming composition formed in thecoating step is heated after to dry the coating layer (heating anddrying step). The heating and drying step can be performed by causingthe non-magnetic support including the coating layer of the non-magneticlayer forming composition to pass through the heated atmosphere. Anatmosphere temperature of the heated atmosphere here can be, forexample, approximately 60° to 140°. Here, the atmosphere temperature maybe a temperature at which the solvent is volatilized and the coatinglayer is dried, and the atmosphere temperature is not limited to therange described above. In addition, the heated air may blow to thesurface of the coating layer. The points described above are alsoapplied to a heating and drying step of a second heating process zoneand a heating and drying step of a third heating process zone which willbe described later, in the same manner.

Next, in a second coating part, the magnetic layer forming compositionis applied onto the non-magnetic layer formed by performing the heatingand drying step in the first heating process zone (coating step ofmagnetic layer forming composition).

After the coating step, a coating layer of the magnetic layer formingcomposition formed in the coating step is cooled in a cooling zone(cooling step). For example, it is possible to perform the cooling stepby allowing the non-magnetic support on which the coating layer isformed on the non-magnetic layer to pass through a cooling atmosphere.An atmosphere temperature of the cooling atmosphere is preferably −10°C. to 0° C. and more preferably −5° C. to 0° C. The time for performingthe cooling step (for example, time while an arbitrary part of thecoating layer is delivered to and sent from the cooling zone(hereinafter, also referred to as a “staying time”)) is not particularlylimited. In a case where the staying time is long, the value oflogarithmic decrement tends to be increased. Thus, the staying time ispreferably adjusted by performing preliminary experiment if necessary,so that the logarithmic decrement equal to or smaller than 0.050 isrealized. In the cooling step, cooled air may blow to the surface of thecoating layer.

After that, while the coating layer of the magnetic layer formingcomposition is wet, an orientation process of the ferromagnetic powderin the coating layer is performed in an orientation zone. For theorientation process, a description disclosed in a paragraph 0052 ofJP2010-24113A can be referred to.

The coating layer after the orientation process is subjected to theheating and drying step in the second heating process zone.

Next, in the third coating part, a back coating layer formingcomposition is applied to a surface of the non-magnetic support on aside opposite to a surface where the non-magnetic layer and the magneticlayer are formed, to form a coating layer (coating step of back coatinglayer forming composition). After that, the coating layer is heated anddried in the third heating process zone.

By doing so, it is possible to obtain the magnetic tape including thecoating layer of the magnetic layer forming composition heated and driedon the non-magnetic layer, on one surface side of the non-magneticsupport, and the back coating layer on the other surface side thereof.The magnetic tape obtained here becomes a magnetic tape product afterperforming various processes which will be described later.

The obtained magnetic tape is wound around the winding part, and cut(slit) to have a size of a magnetic tape product. The slitting isperformed by using a well-known cutter.

In the slit magnetic tape, the burnishing treatment is performed withrespect to the surface of the heated and dried coating layer of themagnetic layer forming composition, before performing the curing process(heating and light irradiation) in accordance with the types of thecuring agent included in the magnetic layer forming composition(burnishing treatment step between heating and drying step and curingstep). The inventors have surmised that removing the pressure sensitiveadhesive component transitioned to the surface and/or the surface layerpart of the coating layer cooled in the cooling zone by the burnishingtreatment contributes setting the logarithmic decrement to be equal toor smaller than 0.050. However, this is merely a surmise, and theinvention is not limited thereto.

The burnishing treatment is treatment of rubbing a surface of atreatment target with a member (for example, a polishing tape, or agrinding tool such as a grinding blade or a grinding wheel), and can beperformed in the same manner as the well-known burnishing treatment formanufacturing a coating type magnetic recording medium. However, in therelated art, the burnishing treatment was not performed in a stagebefore the curing step, after performing the cooling step and theheating and drying step. With respect to this, the logarithmic decrementcan be equal to or smaller than 0.050 by performing the burnishingtreatment in the stage described above.

The burnishing treatment can be preferably performed by performing oneor both of rubbing of the surface of the coating layer of the treatmenttarget by a polishing tape (polishing) and rubbing of the surface of thecoating layer of the treatment target by a grinding tool (grinding). Ina case where the magnetic layer forming composition includes anabrasive, it is preferable to use a polishing tape including at leastone of an abrasive having higher Mohs hardness than that of the abrasivedescribed above. As the polishing tape, a commercially available productmay be used and a polishing tape manufactured by a well-known method maybe used. As the grinding tool, a well-known grinding blade such as afixed blade, a diamond wheel, or a rotary blade, or a grinding wheel canbe used. In addition, a wiping treatment of wiping the surface of thecoating layer rubbed by the polishing tape and/or the grinding tool witha wiping material. For details of preferred polishing tape, grindingtool, burnishing treatment, and wiping treatment, descriptions disclosedin paragraphs 0034 to 0048, FIG. 1 and examples of JP1994-52544A(JP-H06-52544A) can be referred to. As the burnishing treatment isreinforced, the value of the logarithmic decrement tends to bedecreased. The burnishing treatment can be reinforced as an abrasivehaving high hardness is used as the abrasive included in the polishingtape, and can be reinforced, as the amount of the abrasive in thepolishing tape is increased. In addition, the burnishing treatment canbe reinforced as a grinding tool having high hardness is used as thegrinding tool. In regards to the burnishing treatment conditions, theburnishing treatment can be reinforced as a sliding speed between thesurface of the coating layer of the treatment target and a member (forexample, a polishing tape or a grinding tool) is increased. The slidingspeed can be increased by increasing one or both of a speed at which themember is moved, and a speed at which the magnetic tape of the treatmenttarget is moved.

After the burnishing treatment (burnishing treatment step), the curingprocess is performed with respect to the coating layer of the magneticlayer forming composition. In the aspect shown in FIG. 4, the coatinglayer of the magnetic layer forming composition is subjected to thesurface smoothing treatment, after the burnishing treatment and beforethe curing process. The surface smoothing treatment is preferablyperformed by a calender process. For details of the calender process,for example, description disclosed in a paragraph 0026 of JP2010-231843Acan be referred to. As the calender process is reinforced, the surfaceof the magnetic tape can be smoothened. The calender process isreinforced, as the surface temperature (calender temperature) of acalender roll is increased and/or as calender pressure is increased.

After that, the curing process according to the type of the curing agentincluded in the coating layer is performed with respect to the coatinglayer of the magnetic layer forming composition (curing step). Thecuring process can be performed by the process according to the type ofthe curing agent included in the coating layer, such as a heatingprocess or light irradiation. The curing process conditions are notparticularly limited, and the curing process conditions may be suitablyset in accordance with the list of the magnetic layer formingcomposition used in the coating layer formation, the type of the curingagent, and the thickness of the coating layer. For example, in a casewhere the coating layer is formed by using the magnetic layer formingcomposition including polyisocyanate as the curing agent, the curingprocess is preferably the heating process. In a case where the curingagent is included in a layer other than the magnetic layer, a curingreaction of the layer can also be promoted by the curing process here.Alternatively, the curing step may be separately provided. After thecuring step, the burnishing treatment may be further performed.

By doing so, it is possible to obtain a magnetic tape according to oneaspect of the invention. However, the manufacturing method describedabove is merely an example, the magnetic layer surface roughness Ra, thelogarithmic decrement, and the 1-bromonaphthalene contact angle can berespectively controlled to be in the ranges described above by arbitrarymethods capable of adjusting the magnetic layer surface roughness Ra,the logarithmic decrement, and the 1-bromonaphthalene contact angle, andsuch an aspect is also included in the invention.

The magnetic tape according to one aspect of the invention describedabove is generally accommodated in a magnetic tape cartridge and themagnetic tape cartridge is mounted in a drive. The configuration of themagnetic tape cartridge and the drive is well known. The magnetic taperuns (is transported) in the drive, the magnetic head for recordingand/or reproducing of information comes into contact with and slides onthe surface of the magnetic layer, and the recording of the informationon the magnetic tape and/or reproducing of the recorded information areperformed. A running speed of the magnetic tape is also referred to as atransportation speed and is a relative speed of the magnetic tape andthe head at the time of the magnetic tape running. It is preferable thatthe running speed is increased to cause the magnetic tape run at a highspeed, in order to shorten the time necessary for recording informationand/or time necessary for reproducing the recorded information. Fromthis viewpoint, the running speed of the magnetic tape is, for example,preferably equal to or higher than 6.0 m/sec. Meanwhile, it wasdetermined that, in the magnetic tape having the magnetic layer surfaceroughness Ra equal to or smaller than 1.8 nm, a decrease in reproductionoutput occurs, in a case of repeating the high-speed running in theenvironment of a high temperature and high humidity, without anymeasures. With respect to this, in the magnetic tape according to oneaspect of the invention in which the magnetic layer surface roughness Rais equal to or smaller than 1.8 nm and the logarithmic decrement and the1-bromonaphthalene contact angle are in the ranges described above, adecrease in reproduction output during the repeated high-speed runningin the environment of a high temperature and high humidity can beprevented.

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to aspects shown in the examples.“Parts” and “%” in the following description mean “parts by mass” and“mass %”, unless otherwise noted.

As a 1-bromonaphthalene contact angle adjusting agent described below, apolyalkyleneimine-based polymer synthesized by a method disclosed inparagraphs 0115 to 0124 of JP2016-51493A was used.

Example 1

A list of components of each layer forming composition is shown below.

Magnetic Layer Forming Composition

Magnetic Solution

Ferromagnetic hexagonal barium ferrite powder: 100.0 parts

-   -   (Hc: 196 kA/m (2,460 Oe), average particle size (average plate        diameter): 24 nm)

Oleic acid: 2.0 parts

A vinyl chloride copolymer (MR-104 manufactured by Zeon Corporation):10.0 parts

SO₃Na group-containing polyurethane resin: 4.0 parts

-   -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.07        meq/g)

1-Bromonaphthalene contact angle adjusting agent: 10.0 parts

Methyl ethyl ketone: 150.0 parts

Cyclohexanone: 150.0 parts

Abrasive Liquid

α-alumina (Brunauer-Emmett-Teller (BET) specific surface area: 19 m²/g,sphericity: 1.4): 6.0 parts

SO₃Na group-containing polyurethane resin

-   -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.1        meq/g): 0.6 parts

2,3-Dihydroxynaphthalene: 0.6 parts

Cyclohexanone: 23.0 parts

Projection Formation Agent Liquid

Colloidal silica (average particle size: see Table 1, coefficient ofvariation: 7%, sphericity: 1.03): 2.0 parts

Methyl ethyl ketone: 8.0 parts

Other components

Stearic acid: see Table 1

Stearic acid amide: 0.3 parts

Butyl stearate: 6.0 parts

Methyl ethyl ketone: 110.0 parts

Cyclohexanone: 110.0 parts

Polyisocyanate (CORONATE (registered trademark) L manufactured by NipponPolyurethane Industry Co., Ltd.): 3.0 parts

Non-Magnetic Layer Forming Composition

Carbon black (average particle size: 16 nm, dibutyl phthalate (DBP) oilabsorption: 74 cm³/100 g): 100.0 parts

Trioctylamine: 4.0 parts

A vinyl chloride copolymer (MR-104 manufactured by Zeon Corporation):19.0 parts

SO₃Na group-containing polyurethane resin

-   -   (Weight-average molecular weight: 50,000, SO₃Na group: 0.07        meq/g): 12.0 parts

Methyl ethyl ketone: 370.0 parts

Cyclohexanone: 370.0 parts

Stearic acid: 2.0 parts

Stearic acid amide: 0.3 parts

Butyl stearate: 2.0 parts

Back Coating Layer Forming Composition A

Red oxide (average particle size: 0.15 μm, average acicular ratio: 7,BET specific surface area: 52 m²/g): 80.0 parts

Carbon black (average particle size: 16 nm, DBP oil absorption: 74cm³/100 g): 20.0 parts

Phenylphosphonic acid: 3.0 parts

A vinyl chloride copolymer (MR-104 manufactured by Zeon Corporation):12.0 parts

SO₃Na group-containing polyurethane resin

-   -   (Weight-average molecular weight: 50,000, SO₃Na group: 0.07        meq/g): 8.0 parts

α-alumina (BET specific surface area: 17 m²/g): 5.0 parts

Methyl ethyl ketone: 370.0 parts

Cyclohexanone: 370.0 parts

Stearic acid: 1.0 part

Stearic acid amide: 0.3 parts

Butyl stearate: 2.0 parts

Polyisocyanate (CORONATE L manufactured by Nippon Polyurethane IndustryCo., Ltd.): 5.0 parts

1. Manufacturing of Magnetic Tape

Preparation of Magnetic Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

The components of the magnetic solution were kneaded and diluted by anopen kneader, and subjected to a dispersion process of 30 passes, with atransverse beads mill dispersing device and zirconia (ZrO₂) beads(hereinafter, referred to as “Zr beads”) having a particle diameter of0.1 mm by setting a bead filling percentage as 80 volume %, acircumferential speed of rotor distal end as 10 m/sec, and a retentiontime for 1 pass as 2 minutes.

The components of the abrasive liquid were mixed with each other and putin a transverse beads mill dispersing device together with Zr beadshaving a particle diameter of 0.3 mm, bead volume/(abrasive liquidvolume+bead volume) was adjusted to be 80%, and beads mill dispersionprocess was performed for 120 minutes. Liquid after the process wasextracted and subjected to an ultrasonic dispersion filtering processwith a flow-type ultrasonic dispersion filtering device to obtainabrasive liquid.

The magnetic solution, the projection formation agent liquid, and theabrasive liquid, and other components described above were introducedinto a dissolver stirrer, and were stirred at a circumferential speed of10 m/sec for 30 minutes. After that, the treatment of 3 passes wasperformed with a flow-type ultrasonic dispersion device at a flow rateof 7.5 kg/min, and then, a magnetic layer forming composition wasprepared by performing filtering with a filter having a hole diameter of1 μm.

Preparation of Non-Magnetic Layer Forming Composition

The non-magnetic layer forming composition was prepared by the followingmethod.

The components excluding a lubricant (stearic acid, stearic acid amide,and butyl stearate) were kneaded and diluted by an open kneader, andsubjected to a dispersion process with a transverse beads milldispersing device. Then, the lubricant (stearic acid, stearic acidamide, and butyl stearate) was added into the obtained dispersion liquidand stirred and mixed with a dissolver stirrer, and the non-magneticlayer forming composition was prepared.

Preparation of Back Coating Layer Forming Composition

The back coating layer forming composition was prepared by the followingmethod.

The components excluding polyisocyanate and lubricant (stearic acid,stearic acid amide, and butyl stearate) were introduced into a dissolverstirrer, and were stirred at a circumferential speed of 10 m/sec for 30minutes. After that, the dispersion process was performed with atransverse beads mill dispersing device. The polyisocyanate andlubricant (stearic acid, stearic acid amide, and butyl stearate) wereadded into the obtained dispersion liquid and stirred and mixed with adissolver stirrer, and the back coating layer forming composition wasprepared.

Manufacturing of Magnetic Tape

A magnetic tape was manufactured by the specific aspect shown in FIG. 4.The magnetic tape was specifically manufactured as follows.

A support made of polyethylene naphthalate having a thickness of 4.50 μmwas sent from the sending part, and the non-magnetic layer formingcomposition was applied to one surface thereof so that the thicknessafter the drying becomes 0.40 μm in the first coating part and was driedin the first heating process zone (atmosphere temperature of 100° C.) toform a coating layer.

Then, the magnetic layer forming composition was applied onto thenon-magnetic layer so that the thickness after the drying becomes 60 nm(0.06 μm) in the second coating part, and a coating layer was formed.The cooling step was performed by passing the formed coating layerthrough the cooling zone in which the atmosphere temperature is adjustedto 0° C. for the staying time shown in Table 1 while the coating layeris wet, a homeotropic alignment process was performed in the orientationzone by applying a magnetic field having a magnetic field strength of0.3 T in a vertical direction, and then, the coating layer was dried inthe second heating process zone (atmosphere temperature of 100° C.).

After that, in the third coating part, the back coating layer formingcomposition was applied to the surface of the support made ofpolyethylene naphthalate on a side opposite to a surface where thenon-magnetic layer and the magnetic layer are formed, so that thethickness after the drying becomes 0.60 μm, to form a coating layer, andthe formed coating layer was dried in the third heating process zone(atmosphere temperature of 100° C.).

The magnetic tape obtained as described above was slit to have a widthof ½ inches (0.0127 meters), and the burnishing treatment and the wipingtreatment were performed with respect to the surface of the coatinglayer of the magnetic layer forming composition. The burnishingtreatment and the wiping treatment were performed by using acommercially available polishing tape (product name: MA22000manufactured by Fujifilm Corporation, abrasive: diamond/Cr₂O₃/red oxide)as the polishing tape, a commercially available sapphire blade(manufactured by Kyocera Corporation, a width of 5 mm, a length of 35mm, and a tip angle of 60 degrees) as the grinding blade, and acommercially available wiping material (product name: WRP736manufactured by Kuraray Co., Ltd.) as the wiping material, in atreatment device having a configuration disclosed in FIG. 1 ofJP1994-52544A (JP-H06-52544A). For the treatment conditions, thetreatment conditions disclosed in Example 12 of JP1994-52544A(JP-H06-52544A).

After the burnishing treatment and the wiping treatment, a calenderprocess (surface smoothing treatment) was performed with a calender rollconfigured of only a metal roll, at a speed of 80 m/min, linear pressureof 300 kg/cm (294 kN/m), and a calender temperature (surface temperatureof a calender roll) shown in Table 1.

After that, a heating process (curing process) was performed in theenvironment of the atmosphere temperature of 70° C. for 36 hours.

By doing so, a magnetic tape of Example 1 was manufactured.

The thickness of each layer of the manufactured magnetic tape wasacquired by the following method and it was confirmed that the acquiredthickness is the thickness described above.

A cross section of the magnetic tape in a thickness direction wasexposed to ion beams and the exposed cross section was observed with ascanning electron microscope. Various thicknesses were obtained as anarithmetical mean of thicknesses obtained at two portions in thethickness direction in the cross section observation.

Examples 2 to 7 and Comparative Examples 1 to 7

A magnetic tape was manufactured by the same method as that in Example1, except that various conditions were changed as shown in Table 1.

In Table 1, in the examples and the comparative examples in which “used”was shown in the column of the 1-bromonaphthalene contact angleadjusting agent, the same amount of the same 1-bromonaphthalene contactangle adjusting agent was used in the same manner as in Example 1. InTable 1, in the comparative examples in which “none” was shown in thecolumn of the 1-bromonaphthalene contact angle adjusting agent, apolyalkyleneimine-based polymer used in Example 1 as the1-bromonaphthalene contact angle adjusting agent was not used.

In Table 1, in the comparative examples in which “not performed” isdisclosed in a column of the cooling zone staying time and a column ofthe burnishing treatment before the curing process, and “performed” isdisclosed in a column of the burnishing treatment after the curingprocess, a magnetic tape was manufactured by a manufacturing step notincluding the cooling zone in the magnetic layer forming step andperforming the burnishing treatment and the wiping treatment by the samemethod as that in Example 1, not before the curing process, but afterthe curing process.

A part of each magnetic tape of the examples and the comparativeexamples manufactured by the method described above was used in theevaluation described below, and the other part was used in theevaluation of performance which will be described later.

2. Evaluation of Physical Properties of Magnetic Tape

(1) Center Line Average Surface Roughness Ra Measured Regarding Surfaceof Magnetic Layer

The measurement regarding a measurement area of 40 μm×40 μm in thesurface of the magnetic layer of each magnetic tape of the examples andthe comparative examples was performed with an atomic force microscope(AFM, Nanoscope 4 manufactured by Veeco Instruments, Inc.) in a tappingmode, and a center line average surface roughness Ra was acquired.RTESP-300 manufactured by BRUKER is used as a probe, a scan speed (probemovement speed) was set as 40 μm/sec, and a resolution was set as 512pixel×512 pixel.

(2) Measurement of Logarithmic Decrement

The logarithmic decrement of the surface of the magnetic layer of themagnetic tape was acquired by the method described above by using arigid-body pendulum type physical properties testing instrumentRPT-3000W manufactured by A&D Company, Limited (pendulum: brass,substrate: glass substrate, a rate of temperature increase of substrate:5° C./min) as the measurement device. A measurement sample cut out fromthe magnetic tape was placed on a glass substrate having a size ofapproximately 3 cm×approximately 5 cm, by being fixed at 4 portions witha fixing tape (Kapton tape manufactured by Du Pont-Toray Co., Ltd.) asshown in FIG. 1. An adsorption time was set as 1 second, a measurementinterval was set as 7 to 10 seconds, a displacement-time curve was drawnregarding the 86-th measurement interval, and the logarithmic decrementwas acquired by using this curve. The measurement was performed in theenvironment of relative humidity of approximately 50%.

(3) Measurement of 1-Bromonaphthalene Contact Angle

The 1-bromonaphthalene contact angle was measured regarding the surfaceof the magnetic layer by the following method by using a contact anglemeasuring device (contact angle measuring device Drop Master 700manufactured by Kyowa Interface Science Co., Ltd.).

A tape sample obtained by cutting a certain length of the magnetic tapewound in a roll shape from an edge of the roll was placed on slide glassso that the surface of the back coating layer comes into contact withthe surface of the slide glass. 2.0 μl of a liquid for measurement(1-bromonaphthalene) was dropped on the surface of the tape sample(surface of the magnetic layer), formation of stable liquid droplet fromthe dropped liquid was visually confirmed, a liquid droplet image wasanalyzed by contact angle analysis software FAMAS attached to thecontact angle measurement device, and a contact angle formed by the tapesample and the liquid droplet was measured. The calculation of thecontact angle was performed by a θ/2 method, an average value measuredregarding 1 sample six times was set as the 1-bromonaphthalene contactangle. The measurement was performed in the environment of an atmospheretemperature of 25° C. and relative humidity of 25%, and the contactangle was obtained under the following analysis conditions.

Method: liquid droplet method (θ/2 method)

Droplet landing confirmation: automatic

Droplet landing confirmation line (distance from needle tip): 50 dot

Algorithm: automatic

Image mode: frame

Threshold level: automatic

3. Evaluation of Performance of Magnetic Tape

(1) Electromagnetic Conversion Characteristics (Signal-to-Noise-Ratio(SNR)) and Amount of Reproduction Output During Repeated High-SpeedRunning in Environment of High Temperature and High Humidity

Regarding each magnetic tape of the examples and the comparativeexamples, the electromagnetic conversion characteristics (SNR) and theamount of a decrease in reproduction output during the repeated runningwere measured by the following method by using a reel tester having awidth of ½ inches (0.0127 meters) and including a fixed head. Themeasurement was performed in an environment of an atmosphere temperatureof 32° C. and relative humidity of 80%.

A head/tape relative speed was set as 8.0 m/sec, a metal-in-gap (MIG)head (gap length of 0.15 μm, track width of 1.0 μm) was used as therecording head, and a recording current was set as an optimal recordingcurrent of each tape. As a reproducing head, a giant-magnetoresistive(GMR) head having an element thickness of 15 nm, a shield interval 0.1μm, and a lead width of 0.5 μm was used. A signal having linearrecording density of 300 kfci was recorded and measurement regarding areproduction signal was performed with a spectrum analyzer manufacturedby Shibasoku Co., Ltd. The unit, kfci, is a unit of linear recordingdensity (not able to convert to the SI unit system). Regarding thesignal, a signal which was sufficiently stabilized after starting therunning of the magnetic tape was used. Under the conditions describedabove, the sliding of 500 passes was performed by sliding 1,000 m per 1pass to perform the recording and reproducing. A ratio of an outputvalue of a carrier signal and integrated noise of the entire spectralrange was set as an SNR. Regarding the SNR of the first pass,Broadband-SNR (BB-SNR) was shown in Table 1 as a relative value in acase where the value of Comparative Example 1 was set as a reference (0dB).

An output value of a carrier signal of the first pass and an outputvalue of a carrier signal of 500-th pass were respectively obtained, anda difference of “(output value of 500-th pass)−(output value of firstpass)” was shown in Table 1 as the amount of a decrease in reproductionoutput during the repeated running.

(2) Evaluation of Amount of Head Attached Materials

After the measurement in the section (2), the surface of the reproducinghead after reciprocating of 500 passes was observed with a differentialinterference microscope, and the amount of head attached materials wasdetermined with the following criteria, in accordance with the size ofthe area in which the attached materials were confirmed in a microscopicimage obtained with the differential interference microscopeobservation.

5 points: Substantially no head attached materials were observed.

4 points: a slight amount of head attached materials was observed.

3 points: Head attached materials were observed (the amount thereof isgreater than that in a case of 4 points and smaller than that in a caseof 2 points).

2 points: A large amount of head attached materials was observed.

1 point: An extremely large amount of head attached materials wasobserved.

The results described above are shown in Table 1.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Colloidal silica average particle size (nm) 80 80 80 80 80 8040 Calender temperature (° C.) 110 110 110 110 110 110 90 Cooling zonestaying time 1 second 5 seconds 60 180 1 second 1 second 60 secondsseconds seconds Burnishing treatment before curing process PerformedPerformed Performed Performed Performed Performed Performed Burnishingtreatment after curing process Not Not Not Not Not Not Not performedperformed performed performed performed performed performed Magneticlayer forming 1-Bromonaphthalene contact angle Used Used Used Used UsedUsed Used composition adjusting agent Amount of stearic acid (part) 2.52.5 2.5 2.5 3 3.5 3.5 Magnetic layer Center line average surface 1.7 1.71.7 1.7 1.7 1.7 1.5 roughness Ra (nm) Logarithmic decrement 0.048 0.0400.032 0.014 0.048 0.047 0.030 1-Bromonaphthalene contact angle 46.0 46.046.0 46.3 50.0 53.0 53.0 (°) BB-SNR (dB) 3.3 3.2 3.2 3.3 3.2 3.2 4.1Head contamination (large: 1 ⇔ 5: small) 5 5 5 5 5 5 5 Decrease inreproduction output (dB) −0.8 −0.6 −0.4 −0.3 −0.6 −0.5 −0.5 Com- Com-Com- Com- Com- parative parative parative parative parative ComparativeComparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Colloidal silica average particle size (nm) 120 80 80 80 80 8080 Calender temperature (° C.) 110 110 110 110 110 110 110 Cooling zonestaying time Not Not 1 second 60 180 Not Not performed performed secondsseconds performed performed Burnishing treatment before curing processNot Not Performed Performed Performed Not Not performed performedperformed performed Burnishing treatment after curing process PerformedPerformed Not Not Not Performed Performed performed performed performedMagnetic layer forming 1-Bromonaphthalene contact angle None None NoneNone None Used Used composition adjusting agent Amount of stearic acid(part) 1.5 1.5 1.5 1.5 1.5 2.5 3.5 Magnetic layer Center line averagesurface 2.2 1.7 1.7 1.7 1.7 1.7 1.7 roughness Ra (nm) Logarithmicdecrement 0.062 0.060 0.048 0.030 0.015 0.063 0.062 1-Bromonaphthalenecontact angle 42.1 41.9 42.0 42.0 42.0 46.2 52.9 (°) BB-SNR (dB) 0 3.23.3 3.2 3.3 3.2 3.2 Head contamination (large: 1 ⇔ 5: small) 5 1 2 3 4 23 Decrease in reproduction output (dB) −0.8 −4.0 −2.6 −2.1 −1.9 −2.6−2.3

From results shown in Table 1, it is possible to confirm that themagnetic tapes of Examples show a high SNR and in which a decrease inreproduction output during repeated high-speed running under anenvironment of a high temperature and high humidity is small.

The invention is effective in technical fields of magnetic tapes used asrecording media for data storage.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; and a magnetic layer including ferromagnetic powder and abinding agent on the non-magnetic support, wherein a center line averagesurface roughness Ra measured regarding a surface of the magnetic layeris equal to or smaller than 1.8 nm, a logarithmic decrement acquired bya pendulum viscoelasticity test performed regarding the surface of themagnetic layer is equal to or smaller than 0.050, and a contact anglewith respect to 1-bromonaphthalene measured regarding the surface of themagnetic layer is 45.0° to 55.0°.
 2. The magnetic tape according toclaim 1, wherein the logarithmic decrement is 0.010 to 0.050.
 3. Themagnetic tape according to claim 1, wherein the center line averagesurface roughness Ra is 1.2 nm to 1.8 nm.
 4. The magnetic tape accordingto claim 2, wherein the center line average surface roughness Ra is 1.2nm to 1.8 nm.
 5. The magnetic tape according to claim 1, wherein thecontact angle with respect to the 1-bromonaphthalene measured regardingthe surface of the magnetic layer is 45.0° to 53.0°.
 6. The magnetictape according to claim 2, wherein the contact angle with respect to the1-bromonaphthalene measured regarding the surface of the magnetic layeris 45.0° to 53.0°.
 7. The magnetic tape according to claim 3, whereinthe contact angle with respect to the 1-bromonaphthalene measuredregarding the surface of the magnetic layer is 45.0° to 53.0°.
 8. Themagnetic tape according to claim 4, wherein the contact angle withrespect to the 1-bromonaphthalene measured regarding the surface of themagnetic layer is 45.0° to 53.0°.
 9. The magnetic tape according toclaim 1, wherein the magnetic layer includes a nitrogen-containingpolymer.
 10. The magnetic tape according to claim 1, wherein themagnetic layer includes one or more lubricants selected from the groupconsisting of fatty acid, fatty acid ester, and fatty acid amide. 11.The magnetic tape according to claim 1, further comprising: anon-magnetic layer including non-magnetic powder and a binding agentbetween the non-magnetic support and the magnetic layer.
 12. Themagnetic tape according to claim 1, further comprising: a back coatinglayer including non-magnetic powder and a binding agent on a surfaceside of the non-magnetic support opposite to a surface side providedwith the magnetic layer.